The invention relates to a ventilation assembly for a motor vehicle.
The majority of vehicles are equipped with a ventilation assembly which comprises a single motor fan unit intended for cooling the engine block. However, some vehicles must have available a considerable cooling ventilation power, which necessitates the use of two motor fan units.
Ventilation assemblies for motor vehicles are already known which comprise first and second electrically-powered motor fan units, each having a respective maximum operating power, and a control device adapted to vary the ventilation power developed by the assembly formed by the two motor fan units according to a desired total power value.
In these known ventilation assemblies, the control of the two motor fan units is effected either discontinuously, the motor fan units being supplied with power by way of switched resistive circuits, or continuously, in which case provision is made to use an electronic power variation device for each motor fan unit or to use only one electronic power variation device by connecting the two motor fan units in parallel.
In the case of discontinuous control, access can be had to only a limited number of speeds and therefore of ventilation powers.
In the case of control with continuous variation of known type, the use of two electronic power variation devices entails a significant extra cost which is not generally compatible with the price levels aimed for in the motor vehicle industry.
On the other hand, the association in parallel of two motor fan units controlled by a single electronic variator raises vibro-acoustic problems due to beating since the two motor fan units are almost identical. Whichever motor fan units are used, problems of electromagnetic radiation also arise due to the use, by the electronic variators, of chopped current with variable cyclical ratio at high frequency. The transport of this current between the two motor fan units consequently necessitates the use of shielding or filtering devices.
A principal aim of the invention is to propose a ventilation assembly with two motor fan units in which the total power is variably controlled continuously, thus remedying the aforesaid drawbacks.
To this end, according to the invention, the control device comprises an electric power variator with continuous power variation, connected to the first motor fan unit, and a means for cutting-off the supply of the second motor fan unit, the power developed by the said second motor fan unit being either zero or equal to its maximum operating power.
According to other features of the invention:
the control device comprises an electronic calculating device which receives at the input an input desired value signal signifying the desired total ventilation power, and delivers at the output, on the one hand an output desired value signal to the variator, signifying the desired ventilation power of the first motor fan unit, and on the other hand a control signal to the cut-off means, signifying the desired state of the second motor fan unit, the sum of the desired power of the first motor fan unit and of the power developed by the second motor fan unit being equal to the desired total power;
over a low speed operating range, corresponding to desired total power values below a predetermined first threshold value, the desired power of the first motor fan unit is equal to the desired total power, while the signal for control of the cut-off means is a cut-off signal, the maximum operating power of the first motor fan unit being greater than the ventilation power corresponding to the first threshold value;
over a high speed operating range, corresponding to desired total power values above a predetermined second threshold value, the signal for control of the cut-off means is a supply signal, while the desired power of the first motor fan unit is equal to the desired total power reduced by the value of the maximum operating power of the second motor fan unit, said maximum power being less than the desired total power at the point of operation corresponding to the second threshold value;
at a point of operation of the range of desired total power values comprised between the two threshold values, the desired power of the first motor fan unit is:
either equal to the desired total power while the signal for controlling the cut-off means is a cut-off signal, in the case where said point of operation is reached when the second motor fan unit is not supplied;
or equal to the desired total power reduced by the maximum operating power of the second motor fan unit while the signal for controlling the cut-off means is a supply signal, in the case where said point of operation is reached when the second motor fan unit is supplied;
the power corresponding to the first threshold value is between the maximum operating power of the second motor fan unit and the average of the maximum powers of the two motor fan units;
the power corresponding to the second threshold value is between the average of the maximum powers of the two motor fan units and the maximum operating power of the first motor fan unit;
the ratio of the power corresponding to the first threshold value, to the maximum operating power of the first motor fan unit is between 0.65 and 0.75;
the ratio of the power corresponding to the second threshold value, to the maximum operating power of the first motor fan unit is between 0.85 and 0.95; and
the maximum operating power of the second motor fan unit is selected from a range of values between 0.5 and 0.8 times the maximum operating power of the first motor fan unit.
Another aim of the invention is a method for controlling a ventilation assembly as described previously, in which the following steps are carried out:
the desired total power is compared with a second threshold value;
if the desired total power is above the said second threshold value, the second motor fan unit is supplied at its maximum operating power, and the first motor fan unit at a power equal to the desired total power reduced by the maximum operating power of the second motor fan unit;
if the desired total power is below the second threshold value, the desired total power is compared with a first threshold value;
if in addition the desired total power is below the said first threshold value S1, the first motor fan unit is supplied at a power equal to the desired total power and the second motor fan unit is not supplied;
if on the contrary the desired total power is above the said first threshold value S1,
in the case where the second motor fan unit is not supplied, the first motor fan unit is supplied at a power equal to the desired total power and the second motor fan unit is not supplied, and
in the case where the second motor fan unit is supplied, the first motor fan unit is supplied at a power equal to the desired total power reduced by the maximum operating power of the second motor fan unit and the second motor fan unit is supplied at its maximum power.